A number of institutional and industrial operations produce aqueous effluent contaminated with substantial proportions of hydrophobic organic soils. Such soils are commonly found in the waste stream as emulsified droplets dispersed in the waste stream. Such emulsions are commonly stabilized by the presence of one or more surfactants that are part of the effluent material. Commonly, nonionic surfactants act as stabilizing agents. Such waste streams are most commonly a result of the disposal of hydrophobic waste or a result of a cleaning operation wherein large quantities of hydrophobic soils are cleaned from environmental surfaces, clothing, rags, dishes and pans, etc. and other hydrophobic soil containing objects. The resulting aqueous effluent can contain substantial proportions of hydrophobic organic soils typically derived from fat, oil and grease. Prior to disposal, the aqueous effluent must be treated to separate such soils before the effluent can be safely discharged into municipal sewer systems.
The use of alkaline cleaning compositions containing inorganic detergent and builder components in combination with organic surfactant compositions and other components have been common for many years in laundry operations. Typical laundry processes involve contacting soiled woven or non-woven fabric with an aqueous cleaning composition containing proportions of laundry chemicals dissolved or suspended in the aqueous medium. The organic and inorganic chemicals cooperate to remove soil from fabric. The soils become suspended by the cleaning chemicals in the aqueous through the action of the active chemical cleaners.
In commercial laundry operations soil load and soil type can create substantial operating difficulties. A substantial proportion of the laundry workload will constitute items contaminated with such hydrophobic organic soil. Such items include mechanics' clothing, shop wipes, shop towels, contaminated uniforms, drop cloths, machine covers, mop heads, and other units typically manufactured from either synthetic or natural fibers woven or otherwise assembled into typically flexible units that can be soaked or saturated with substantial quantities of the hydrophobic organic soils. The hydrophobic organic soils typically involved in the cleaning methods and compositions of this invention comprise fats, oils and grease. Fats are typically organic materials derived from natural sources such as animals and plants. Fats are typically liquid or solid fatty acid glycerol esters, phospholipids, etc. and are typically produced in food processing but also have a number of industrial uses. Oils are commonly liquids produced from petroleum refining but can also include materials such as liquid vegetable oil, silicone oil, etc. Greases are commonly considered to be a heavy, thick solid or semisolid hydrocarbon or suspensions of organic or inorganic solid particulate materials in a fat or oil base. Greases are typically substantially semisolid or solid materials used in lubrication purposes. Commonly such hydrophobic organic soils are generated in kitchen, bar or other food service environments, in shop environments such as printing shops, metal working shops, auto repair shops, fast food outlets, restaurants, etc. In the operations of such installations, substantial quantities of fats, oils and greases are used in operation and can come in contact with walls and floors of the installation and the clothing worn by employees. The environment of the installations are commonly cleaned using mops, shop towels, bar towels, bar mops, kitchen rags, wipes, rags and other cleaning instruments. The soil load can be as much as 20 wt-%, typically 5 wt-% to 17 wt-%, on the fabric.
Municipal, county, state and federal regulations often place stringent requirements on the concentration of a variety of contaminants in effluent. After laundering soiled items, the substantial quantity of organic soils in laundry effluent is often unacceptable environmentally due to the presence of up to 2000 ppm hydrophobic soil and often more. In the production of effluent from commercial laundries, fats, oils and greases are often required to be substantially less than 250 ppm and often between 10 and 100 ppm as measured by EPA analytical method 180.1.
Efficient laundry chemicals in aqueous media remove hydrophobic soils by creating a emulsion of the soil in the aqueous medium. The emulsion comprises small hydrophobic droplets sometimes called micelles which are surrounded and stabilized by the detergent or surfactant materials. The dispersed nature of the soil in aqueous medium is a substantial barrier to its removal after laundering. Before removal can be obtained, the micelle must be destabilized, the emulsion must be broken, the fats, oils and greases must be reassembled into a single phase and the single phase hydrophobic material must be separated from the aqueous solution. A number of methods for separating fats, oils and greases from laundry effluent have been attempted. One useful alternative involves changing the pH of the wash medium from neutral or mildly alkaline to acid to break the emulsion of the organic hydrophobic soil. Once the emulsion is broken, a separate phase of hydrophobic soil forms which can be readily removed.
Boettner et al., U.S. Pat. No. 3,117,999, teach a tertiary carbonimine substituted with both ethylene oxide and propylene oxide blocks to form nonionic surfactant materials. Dupre et al., U.S. Pat. No. 3,118,000, teach alkylamine compositions substituted with both ethylene oxide and propylene oxide blocks to produce nonionic surfactant material. Maloney et al., U.S. Pat. No. 4,605,773, teach a low foaming pH sensitive alkyl amine polyether surfactant that can be used in production of paper from recycled secondary fiber. The disclosed surfactants are pH sensitive and have substantial surfactant properties. Cohen, U.S. Pat. No. 5,110,503, teaches compositions and methods for cleaning hydrophobic organic soil containing contaminated fabric with methods of separating the hydrophobic soil from laundry effluent. Cohen uses a composition of matter comprising a first component, comprising a reaction product of an .alpha.,.beta.-unsaturated acid and a short chain amine such as a .beta.-amino dipropionic acid, having an assigned structure as RN(CH.sub.2 CH.sub.2 CO.sub.2 H).sub.2, with a variety of ether surfactants such as an ethoxylate- propoxylate block copolymer, sulfates or sulfonates, alkoxylated phosphates. Lastly, McFarlan et al., U.S. Pat. No. 5,207,922, is primarily directed to a method of treating laundry effluent or wastewater for the purpose of separating fats, oils and greases. At Column 3, lines 19-60, McFarlan et al. teach typical laundry chemical compositions.
The comparative ability for separating hydrophobic organic soils such as fats, oils and greases from laundry effluent is typically characterized by the concentration of the chemicals used in the laundry, the pH at which the phase separation occurs, the rate of the phase separation and the final concentration in the aqueous effluent of hydrophobic soil such as residual fats, oils and greases. The degree of separation is pH sensitive. Reducing the pH as low as 2 can cause a clean break, however, such a low pH requires substantial amounts of acid and also exposes operating equipment and personnel to unacceptably low pH. Further, even at such low pH's some compositions fail to reach an acceptable level of fats, oils and greases in effluent. We have found in our work with pH sensitive laundry chemical systems that many such prior art systems have an unacceptably low pH requirement to obtain a clean separation or fail to reduce the concentration of fats, oils and greases in the aqueous effluent to a level sufficient to satisfy environmental regulations.
A substantial need continues to exist for a method of reducing the residual concentration of hydrophobic soils in aqueous waste streams using a pH change in a chemical addition protocol. Further, a need exists to improve laundry chemical systems that can be used in cleaning processes involving items having a substantial loading of hydrophobic organic soil in laundry effluent. Systems are needed that produce an effluent that can be treated after laundering to separate fats, oils and greases such that the final concentration in the aqueous effluent is less than 250 ppm and preferably substantially below 100 ppm.